In general, a construction machine such as an excavator performs various workings such as excavation, conveyance and loading. Almost all the workings need to endure a high working load or require high working speed, and need to efficiently distribute a working fluid discharged from a hydraulic pump to working tools. In particular, working tools frequently used for types of workings or working tools requiring high power need to be controlled such that a fluid amount is smoothly supplied to the working tools, in order to enhance working efficiency and increase power efficiency.
As an example, a large amount of working fluid needs to be supplied to a boom cylinder when a boom is raised. However, a working fluid supplied to the boom cylinder is also supplied to an arm cylinder, a bucket cylinder and a pivot motor. For this reason, in order for the boom cylinder to secure a sufficient amount of working fluid, an amount of working fluid supplied to at least one of the arm cylinder, the bucket cylinder and the pivot motor needs to be reduced.
However, when a hydraulic main control valve converted by a pilot pressure is used, it is difficult to determine a working tool to which a working fluid is to be supplied first according to a type of working and fluid amounts for the working tools cannot be adjusted finely. Moreover, separate fluid amount regulating valves connected to various working tool control valves need to be added to adjust the distribution of the fluid amount, but it is difficult to add fluid amount regulating valves due to a narrow installation space of a construction machine and manufacturing costs of the construction machine increase.
Even when the fluid amount regulating valves are added, since a working fluid supplied to working tools needs to pass through the fluid amount regulating valves, power loss due to loss of pressure increases and temperature of the working fluid rises, hampering precision of working.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.